<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
<form action="calc.php">
    <input type="text" name="a"><select name="op">
    <option value="+">加</option>
    <option value="-">减</option>
    <option value="*">乘</option>
    <option value="/">除</option>
</select>
    <input type="text" name="b">
    <input type="submit" value="计算">
</form>
</body>
</html>